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| <!--- | ||
| Licensed to the Apache Software Foundation (ASF) under one | ||
| or more contributor license agreements. See the NOTICE file | ||
| distributed with this work for additional information | ||
| regarding copyright ownership. The ASF licenses this file | ||
| to you under the Apache License, Version 2.0 (the | ||
| "License"); you may not use this file except in compliance | ||
| with the License. You may obtain a copy of the License at | ||
| http://www.apache.org/licenses/LICENSE-2.0 | ||
| Unless required by applicable law or agreed to in writing, | ||
| software distributed under the License is distributed on an | ||
| "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | ||
| KIND, either express or implied. See the License for the | ||
| specific language governing permissions and limitations | ||
| under the License. | ||
| --> | ||
| Apache Flume: How to Contribute | ||
| =============================== | ||
|
|
||
| Welcome contributors! We strive to include everyone's contributions. | ||
| This page provides necessary guidelines on how to contribute effectively | ||
| towards furthering the development and evolution of Flume. You should | ||
| also read the guide on setting up Development Environment where you will find | ||
| details on how to checkout, build and test Flume. | ||
|
|
||
| **Note**: This guide applies to general contributors. If you are a | ||
| committer, please read the How to Commit guide as well. | ||
|
|
||
|
|
||
| What can be contributed? | ||
| ------------------------ | ||
|
|
||
| There are many ways you can contribute towards the project. A few of | ||
| these are: | ||
|
|
||
| **Jump in on discussions**: It is possible that someone initiates a | ||
| thread on the mailing list describing a problem that you have dealt with | ||
| in the past. You can help the project by chiming in on that thread and | ||
| guiding that user to overcome or workaround that problem or limitation. | ||
|
|
||
| **File Bugs**: If you notice a problem and are sure it is a bug, then go | ||
| ahead and [file a JIRA](https://issues.apache.org/jira/browse/Flume). If | ||
| however, you are not very sure that it is a bug, you should first | ||
| confirm it by discussing it on the [Mailing | ||
| Lists](https://cwiki.apache.org/confluence/display/FLUME/Mailing+Lists). | ||
|
|
||
| **Review Code**: If you see that a JIRA ticket has a "Patch Available" | ||
| status, go ahead and review it. It cannot be stressed enough that **you | ||
| must be kind in your review** and explain the rationale for your | ||
| feedback and suggestions. Also note that not all review feedback is | ||
| accepted - often times it is a compromise between the contributor and | ||
| reviewer. If you are happy with the change and do not spot any major | ||
| issues, then `+1` it. More information on this is available in the | ||
| following sections. | ||
|
|
||
| **Provide Patches**: We encourage you to assign the relevant JIRA issue | ||
| to yourself and supply a patch for it. The patch you provide can be | ||
| **code**, **documentation**, **build changes**, or any combination of | ||
| these. More information on this is available in the following sections. | ||
|
|
||
| Providing Patches | ||
| ----------------- | ||
|
|
||
| In order to provide patches, follow these guidelines: | ||
|
|
||
| - **Make sure there is a JIRA**: | ||
| 1. If you are working on fixing a problem that already has an | ||
| associated JIRA, then go ahead and assign it to yourself. | ||
| 2. If it is already assigned to someone else, check with the | ||
| current assignee before moving it over to your queue. | ||
| 3. If the current assignee has already worked out some part of the | ||
| fix, suggest that you can take that change over from them and | ||
| complete the remaining parts. | ||
|
|
||
|
|
||
|
|
||
| - **Attach the patches as you go through development**: | ||
| - While small fixes are easily done in a single patch, it is | ||
| preferable that you attach patches to the JIRA as you go along. | ||
| This serves as an early feedback mechanism where interested | ||
| folks can look it over and suggest changes where necessary. It | ||
| also ensures that if for some reason you are not able to find | ||
| the time to complete the change, someone else can take up your | ||
| initial patches and drive them to completion. | ||
|
|
||
| - **Before you submit your patch**: | ||
| 1. Your change should be well-formatted and readable. Please use | ||
| two spaces for indentation (no tabs). | ||
| 2. Carefully consider whether you have handled all boundary | ||
| conditions and have provided sufficiently defensive code | ||
| where necessary. | ||
| 3. Add one or more unit tests, if your change is not covered by | ||
| existing automated tests. | ||
| 4. Insert javadocs and code comments where appropriate. | ||
| 5. Update the [Flume User | ||
| Guide](http://flume.apache.org/FlumeUserGuide.html) | ||
| ([source](https://git-wip-us.apache.org/repos/asf?p=flume.git;a=blob;f=flume-ng-doc/sphinx/FlumeUserGuide.rst;hb=trunk)) | ||
| if your change affects the Flume config file or any | ||
| user interface. Include those changes in your patch. | ||
| 6. Make sure you update the relevant developer documentation, wiki | ||
| pages, etc. if your change affects the development | ||
| environment. | ||
|
|
||
| - **Test your changes before submitting a review**: | ||
| - Before you make the JIRA status as "Patch Available", please | ||
| test your changes thoroughly. Try any new feature or fix out for | ||
| yourself, and make sure that it works. | ||
| - Make sure that all unit/integration tests are passing, and that | ||
| the functionality you have worked on is tested through existing | ||
| or new tests. | ||
| - You can run all the tests by going to the root level of the | ||
| source tree and typing `mvn clean install`. | ||
|
|
||
| - **How to create a patch file**: | ||
| - The preferred naming convention for Flume patches is | ||
| `FLUME-12345.patch`, or `FLUME-12345-0.patch` where `12345` is | ||
| the JIRA number. You might want to name successive versions of | ||
| the patch something like `FLUME-12345-1.patch`, | ||
| `FLUME-12345-2.patch`, etc. as you iterate on your changes based | ||
| on review feedback and re-submit them. | ||
| - The command to generate the patch is "git diff". Example: | ||
|
|
||
| ``` | ||
| $ git diff > /path/to/FLUME-1234-0.patch | ||
| ``` | ||
| - **How to apply someone else's patch file**: | ||
| - You can apply someone else's patch with the GNU `patch` tool. | ||
| Example: | ||
| ``` | ||
| $ cd ~/src/flume # or wherever you keep the root of your Flume source tree | ||
| $ patch -p1 < FLUME-1234.patch | ||
| ``` | ||
| - Contributors may variously submit patches in a couple of | ||
| different formats. If you get some dialog from the `patch` tool | ||
| asking which file you want to patch, try variously the "-p1" or | ||
| "-p0" flags to `patch`. Without any additional arguments, | ||
| `git diff` generates patches that are applied using `patch -p1`. | ||
| If you use `git diff --no-prefix` to generate your patch, you | ||
| have to apply it using `patch -p0`. The ReviewBoard tool | ||
| understands both formats and is able to apply both | ||
| types automatically. | ||
| - **Submitting your patch for review:** | ||
| 1. To submit a patch, attach the patch file to the JIRA and change | ||
| the status of the JIRA to "Patch Available". | ||
| 2. If the change is non-trivial, please also post it for review on | ||
| the [Review | ||
| Board](https://reviews.apache.org/groups/Flume/). | ||
| Use the Repository "flume-git" on Review Board. | ||
| 3. Link the JIRA to the Review Board review. JIRA has a feature you | ||
| can use for this by going to More Actions > Link > Web | ||
| Link when logged into JIRA. | ||
| - **Identify a reviewer:** | ||
| 1. When posting on [review | ||
| board](https://reviews.apache.org/groups/Flume/) | ||
| (repository: "flume-git"), always add the Group "Flume" to the | ||
| list of reviewers. | ||
| 2. Optionally, you may also add a specific reviewer to the review. | ||
| You can pick any of the project committers for review. Note that | ||
| identifying a reviewer does not stop others from reviewing | ||
| your change. Be prepared for having your change reviewed by | ||
| others at any time. | ||
| 3. If you have posted your change for review and no one has had a | ||
| chance to review it yet, you can gently remind everyone by | ||
| dropping a note on the developer mailing list with a link to | ||
| the review. | ||
| - **Work with reviewers to get your change fleshed out**: | ||
| 1. When your change is reviewed, please engage with the reviewer | ||
| via JIRA or review board to get necessary clarifications and | ||
| work out other details. | ||
| 2. The goal is to ensure that the final state of your change is | ||
| acceptable to the reviewer so that they can +1 it. | ||
| Reviewing Code | ||
| -------------- | ||
| Flume uses the [Apache Review | ||
| Board](https://reviews.apache.org/groups/Flume) for | ||
| doing code reviews. In order for a change to be reviewed, it should be | ||
| either posted on the review board or attached to the JIRA. If the change | ||
| is a minor change affecting only few lines and does not seem to impact | ||
| main logic of the affected sources, it need not be posted on the review | ||
| board. However, if the code change is large or otherwise impacting the | ||
| core logic of the affected sources, it should be posted on the review | ||
| board. Feel free to comment on the JIRA requesting the assignee to post | ||
| the patch for review on review board. | ||
| **Note**: Not all patches attached to a JIRA are ready for review. | ||
| Sometimes the patches are attached just to solicit early feedback | ||
| regarding the implementation direction. Feel free to look it over and | ||
| give your feedback in the JIRA as necessary. Patches are considered | ||
| ready for review either when the patch has been posted on review board, | ||
| or the JIRA status has been changed to 'Patch Available'. Find here a | ||
| [list of Flume JIRAs marked Patch | ||
| Available](https://issues.apache.org/jira/issues/?jql=project%20%3D%20flume%20AND%20status%20%3D%20%22Patch%20Available%22). | ||
| ### Goals for Code Reviews | ||
| The net outcome from the review should be the same - which is to ensure | ||
| the following: | ||
| - Bugs/Omissions/Regressions are caught before the change is committed | ||
| to the source control. | ||
| - The change is subjected to keeping the quality of code high so as to | ||
| make the overall system sustainable. The implementation of the | ||
| change should be easily readable, documented where necessary, and | ||
| must favor simplicity of implementation. | ||
| - Changes are evaluated from the perspective of a consumer | ||
| (the reviewer) as opposed to the developer, which often brings out | ||
| subtleties in the implementation that otherwise go unnoticed. | ||
| - The change should be backward compatible and not require extensive | ||
| work on existing installations in order for it to be consumed. There | ||
| are exceptions to this in some cases like when work is done on a | ||
| major release, but otherwise backward compatibility should be upheld | ||
| at all times. If you are not clear, raise it is as a concern to be | ||
| clarified during the review. | ||
| ### Code review guidelines | ||
| Following are some guidelines on how to do a code review. You may use | ||
| any other approach instead as long as the above stated goals are met. | ||
| That said, here is an approach that works fine generally: | ||
| - **Understand the problem being solved**: This often requires going | ||
| through the JIRA comments and/or mailing list threads where the | ||
| discussion around the problem has happened in the past. Look for key | ||
| aspects of the problem such as how it has impacted the users and | ||
| what, if any, is the suggested way to solve it. You may not find | ||
| enough information regarding the problem in some cases, in which | ||
| case - feel free to ask for clarification from the developer | ||
| contributing the change. | ||
| - **Think about how you would solve the problem**: There are many ways | ||
| to solve any code problem, with different ways having | ||
| different merits. Before proceeding to review the change, think | ||
| through how you would solve the problem if you were the one | ||
| implementing the solution. Note the various aspects of the problem | ||
| that your solution might have. Some such aspects to think about | ||
| are - impact on backward compatibility, overall usability of the | ||
| system, any impact on performance etc. | ||
| - **Evaluate the proposed change in contrast to your solution**: | ||
| Unless the change is obvious, it is likely that the implementation | ||
| of the change you are reviewing is very different from the solution | ||
| you would go for. Evaluate this change on the various aspects that | ||
| you evaluated your solution on in the previous step. See how it | ||
| measures up and give feedback where you think it could be improved. | ||
| - **Look for typical pitfalls**: Read through the implementation to | ||
| see if: it needs to be documented at places where the intention is | ||
| not clear; if all the boundary conditions are being addressed; if | ||
| the code is defensive enough; if any bad idioms have leaked in such | ||
| as double check locking etc. In short, check for things that a | ||
| developer is likely to miss in their own code which are otherwise | ||
| obvious to someone trying to read and understand the code. | ||
| - **See if the change is complete**: Check if the change is such that | ||
| it affects the user interface. If it does, then the documentation | ||
| should likely be updated. What about testing - does it have enough | ||
| test coverage or not? What about other aspects like license headers, | ||
| copyright statements etc. How about checkstyle and findbugs - did | ||
| they generate new warnings? How about compiler warnings? | ||
| - **Test the change**: It is very easy to test the change if you have | ||
| the development environment setup. Run as many tests as | ||
| you want with the patch. Manually test the change for functionality | ||
| that you think is not fully covered via the associated tests. If you | ||
| find a problem, report it. | ||
| ### How to give feedback | ||
| Once you have collected your comments/concerns/feedback you need to send | ||
| it to back to the contributor. In doing so, please be as courteous as | ||
| possible and ensure the following: | ||
| - Your feedback should be clear and actionable. Giving | ||
| subjective/vague feedback does not add any value or facilitate a | ||
| constructive dialog. | ||
| - Where possible, suggest how your concern can be addressed. For | ||
| example if your testing revealed that a certain use-case is not | ||
| satisfied, it is acceptable to state that as is, but it would be | ||
| even better if you could suggest how the developer can address it. | ||
| Present your suggestion as a possible solution rather than | ||
| *the* solution. | ||
| - If you do not understand part of the change, or for some reason were | ||
| not able to review part of the change, state it explicitly so as to | ||
| encourage other reviewers to jump in and help. | ||
| Once you have provided your feedback, wait for the developer to respond. | ||
| It is possible that the developer may need further clarification on your | ||
| feedback, in which case you should promptly provide it where necessary. | ||
| In general, the dialog between the reviewer and developer should lead to | ||
| finding a reasonable middle ground where key concerns are satisfied and | ||
| the goals of the review have been met. | ||
| If a change has met all your criteria for review, please `+1` the change | ||
| to indicate that you are happy with it. |